Transformer



June 8 1926. 1,588,204

H. O. STEPHENS El AL TRANSFORMER Filed Sept. 5, 1925 5 Sheets-Sheet 1Inventors:

Howard 0.5tephens,

Arthur Palme, by .Thei PAttoPney.

June 8 1926. 1,588,204

H. o. STEPHENS ET AL TRANSFORMER Filed Sept. 5, 1925 3 Sheets-Sheet 2 54J6 J3 r, 5

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Howard O.5tephens Arth ur- Palme,

ThQirAttoPney June 8 1926.

H. O. STEPHENS ET AL I TRANSFORMER Filed Sept. 5

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Inventor-s: Howard O.Stephens Arthur alme,

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Patented June 8, 1926.

UNITED STATES 1,588,204 PATENT OFFICE.

HOWARD O. STEPHENS AND ARTHUR PALME, OF PITTSFTELD, MASSACHUSETTS, AS-SIGNORS TO GENERAL ELECTRIC'GOMPANY, A CORPO RATION OF NEW YORK.

TRANSFORMER.

Application filed September 3, 1925. Serial No. 54,366.

our invention relates to transformers and more particularly totransformers having windings with tap connections whereby the effectivenumber of turns may be varied to change the ratio of transformation.Varying conditions in the circuits connected to a transformer often makeit necessary to change the ratio of voltage transformation in thetransformer and the general object of the invention is to produce animproved arrangement of transformer and associated control mechanismwhereby this result may be attained without interrupting the loadcurrent supplied by the transformer.

Other objects and advantages will appear from the following descriptiontaken in connection with the accompanying drawings in which Fig. 1 is aview in elevation of a single phase transformer with part of the controlmechanism; Fig. 2 is an explanatory detail view of part of the controlmechanism; Fig. 3 is a circuit diagram of the control mechanism; Figs. 4and 5 are detail views of part of the control mecha nism; and Fig. 6 isa circuit diagram show ing the application of the invention to athree-phase transformer;

Like reference characters indicate similar parts in the differentfigures of the drawings.

The invention will be dcscribed in con nection with the transformer 10shown in Y Figs. 1 and 2. This transformer is enclosed m a casing 11adapted to hold a body of insulating oil'in which the transformer isimmersed. An expansion chamber 12 com municates with the casing 11 topermit thermal expansion and contraction of the oil and a diaphragm 13in a. relief pipe 13 is adapted to rupture to relieve pressure in thecasing 11 when this pressure becomes excessive.

One of the windings of the transformer 10 is formed in two sections 14and 15, each section being provided with taps connected to the fixedcontacts of switches 16 and 17 respectively. The other winding of thetransformer is not shown in the drawing as it forms no part of theinvention. One

terminal 18 of the tapped winding is connected to both winding sections14 and 15.

The other terminal 19 of this winding is connected to the main contactsof two switches or circuit breakers 20 and 21 and 22 and 23 to themovable contacts of the tap I switches 16 and 17. The two windingsections 14 and 15 are similar so that, during normal operation of thetransformer, the current between the two terminals 18 and 19 dividesinto two equal parts, each part flowing through one of the windingsections and its associated tap switch and circuit breaker.

This arrangement of the parallel connected winding sections 14 and 15with their associated tap switches 16 and 17 and circuit breakers 20 and21 may be operated by control mechanism which will be described tochange the number of effective turns in the winding sections and thusthe ratio of voltage transformation without any interrup tion in theload carried by the transformer. To effect this change, the controlmechanism causes one of the circuit breakers, circuit breaker 20 forexample, to open, thus inter- I rupting the current through the tapswitch rent again divides substantially equally between the two windingsections 14 and 15. There is now an unequal number of effective turnsand consequent unequal voltage in the two sections 14 and 15. Thiscauses a circulating current in these two winding sections, the two tapswitches 16 and 17 and the two circuit breakers 20 and 21 but thereactance of the winding sections prevents this circulating'current fromreaching such a value as to be objectionable. The circuit breaker 21 isnext opened to interrupt the current in the winding section 15 and itstap switch 17, the tap switch 17 is changed to a position correspondingto that of the tap switch 16, and the circuit breaker 21 is then closed.The number of efiective turns has now been increased or decreasedequally in the two winding sections and the steps described may berepeated until the desired increase or decrease in the number ofeflective turns in each winding section has been made. 7

The control mechanism is responsive to a single hand wheel 24 fixed to ashaft which carries a. drum contactor 25 and the driving member 26 of adouble intermittent gear by means of which the two tap switches 16 and17 may be operated intermittently and alternately through the two drivenmembers 27 and 28, two sets of gears 29 and 30, and two bevel gearconnected shafts 31 and 32. The contactor 25 comprises five contacts 33,34, 35, 36 and 37 (shown as developed into a plane in Fig. 3), whichcooperate with four brushes 38, 39, 40 and 41. The contacts are allconductively connected together and to a source of current 42 throughthe brush 38. The circuit breaker .20 is pro: vided with a closing coil43, a tripping coil 44 and two auxiliary contactors 45 and 46. Thecontactor 45 has two pairs of contacts 47 and 48 and the contactor 46has two pairs of contacts 49 and 50. The circuit breaker 21 is similarlyprovided with a closing coil 51, a tripping coil 52, and two contactors53- and 54, the contactor 53 having two pairs of contacts 55 and 56 andthe contactor 54 having two pairs of contacts 57 and 58.

The number of eflective turns in the winding sections 14 and 15 ischanged by turning the hand-wheel 24 in the proper direction, onedirection effecting an increase and the other direction effecting adecrease and the operation of the control mechanismas the hand-wheel 24is turned in a clockwise direction will now be described. Rotation ofthe hand-wheel 24 with the drum contactor 25 through a small angle firstmoves the contact 35 of the drum contactor under the brush 40 and thecontact 37 away from the brush 39. This allows current to flow from thecontact 35 through the brush 40, the contacts 49 of circuit breaker 20and the tripping coil 52 and contacts 55 of the circuit breaker 21, thuscausing the circuit breaker 21 to open and interrupt the current throughthe winding section 15. This opening of the circuit breaker 21 moves itstwo contactors 53 and 54 to open the contacts 55 and 57 and to close thecontacts 56 and 58. Closing the contacts 56 has no effect as the circuitthrough these contacts is now open between the contact 37 and the brush39 of the contactor 25. Closing the contacts 58, however, completes acircuit from the source of current 42 through a releasing coil 59 towithdraw a latch 60 from locking engagementwith the gearing 30. Thefunction of the latch 60 is to act through the gearing 30 and shaft 32to lock the movable contact of the tap switch 1.7 in adjusted posit-ionexcept at such time as the contact is being shifted by the controlmechanism. The driving member 26 of the aeeaaoa double intermittent gearnext engages the driven member 28 and rotates it one step, the .drivenmember 28 acting through the gearing 30 and shaft 32 to shift themovable contact of the tap switch 17 along one step. The contact 34 ofthe drum contactor 25 then moves under the brush 39 to complete acircuit from the source of current 42 through the coil of a time delayrelay 61 and the auxiliary contacts 56 and contactor 53 of the circuitbreaker 21. This closes the contacts of the time delay relay 61 whichcompletes a circuit from the source of current 42 through the closingcoil 51 of the circuit breaker 21. The purpose of the time delay relay61- is to keep the circuit through the closing coil 51 of the circuitbreaker 21 closed long enough to be sure that the circuit breaker willclose properly, thus avoiding the possibility that the contact 34 of thedrum contactor 25 might be moved fast enough to leave the brush 39before the circuit breaker had had time to close.

The closing coils 43 and 51 of the circuit breakers will require aheavier current than that supplied through the contacts and brushes of.the drum contactor 25 and a further advantage of the time delay relays61 and 64 is that they may be conveniently designed with contacts tocarry this heavier current. I

The closing of the circuit breaker 21 connects the winding section 15back in circuit to carry its share of current. The change inv the numberof effective turns in the winding section 15 produces an unbalancebetween the two winding sections and this causes a circulating currentthrough them which is limited to a safe value bythe reactance of thewinding sections.

The hand-wheel 24 has now been turned through half a revolution and thishas caused the movable contact of the tap switch 17 to be shifted onestep in the desired direction. Rotation of the hand-wheel through thesecond half of a complete revolution causes the control mechanism to actin a similar manner to shift the movable contact of the tap switch 16along one step and again balance the two winding sections 14 and 15. Thecontact 36 controls the tripping coil 44 to open the circuit breaker 20,

the contactor 46 closing the contacts 50 as the circuit breaker 20 opensto send current through a releasing coil 62 to withdraw a latch 63 fromlooking engagement with the gearing 29. The I11OVlbl contact of the tapswitch 16 is then shifted one step to a posi tion corresponding to thatof the movable contact of the tap switch 17. The contact 37 of the drumcontactor 25 then moves into its original position under the brush 39 toclose the circuit through a time delay relay 64 and the closing of thecontacts of this relay sends current through the closing coil 3 of thecircuit breaker 20. The closing of this circuit ln'eakcr completes thecycle of operations.

The two conductors 22 and 23 are pro long as the currents in the twoconductors 22 and 28 and in the winding sections 14 and 15- are equal.\Vhenever the currents in the two winding sections 14 and 15 areunequal, however, the voltages of the two current transformers 65 and 66will be unequal and this will operate a relay 67 controlling a signal68. 'lhesignal 68 will thus indicate when either of the circuits throughthe winding sections 14 and 15 is openand the other winding sectionis'carrying all the current and it will also indicate when the movablecontacts of the two tap switches are not similarly positioned so 'thatthe two winding sections 14 and 15 are unbalanced.

The auxiliary contacts 49 of the circuit breaker 20 are always open whenthis circuit breaker is open. These contacts-49 are in circuit with thetripping coil 52 of the other circuit breaker 21 so that the circuitbreaker 21 can never be opened while the circuit 20 is opened. Theauxiliary contacts 57 of the circuit breaker 21 likewise pre ent openingof the circuit breaker 20 when the circuit breaker 21 is open.- Thusonly one circuit breaker can be open at a time and current between thetransformer terminals 18 and 19 can never be interrupted.

The tap switches 16 and 17 are locked by the latches 63 and 60respectively. Each of these latches is controlled by auxiliary contactson its associated circuit breaker so that neither tap switch connectioncan be changed unless its associated circuit is open and thecorresponding winding section is carrying no current. Thus no arcing canever occur at the contacts of the tap switches. This is importantbecause the tap switches are located in the same casing and are immersedin the same insulating oil with the transformer so that the tap leadsfrom the winding sections of the transformer to the tap switches are asshort as possible and require no insulating bushings through the casingas would be necessary were the tap switches located outside the casing.Arcing at the contacts of the tap switches would seriously alieet theinsulating oil in which they and the transformer are immersed but anyarcing that may occur must be at. the contacts of the two circuitbreakers 20 and 21 which are located outside the casing.

The two tap switches are interlocked by the double intermittent gear sothat only one of these switches can be moved at a tlme and so that. theycan never be moved more than one step apart.

The signal (58 will indicate any unbalanced condition between the twowinding sections 14 and 15. It will indicate not only when the number ofefiective turns is not the same in the two winding sections or when thecircuit through one of the winding sections is open at the correspondingcircuit breaker during a tap changing operation, but it will indicateany accident or failure in the transformer or its connections whichunbalances the equal distribution of current between the two windingsections.

It will be obvious that the control mechanism may be operated in eitherdirection through as many cycles as desired within the range of the tapswitches and that the operation may be stopped and reversed in directionat any point in a cycle of opera tion.

-The invention has been described and its advantages pointed out asapplied in connection with a single phase transformer but it may, ofcourse, be applied to a three-phase transformer as indicated in Fig. 6where each phase comprises a winding formed in two sections 14 and 15and connected in parallel between terminals 18 and 19. The two'.

winding sections of each phase are provided with tap switches 16 and 17and circuit breakers 20 and 21 respectively. The ta switches and thecircuit breakers are eac mechanically connected in two groups of threeeach as shown in Fig. 6 so that adjustment of the three hases iseffected simultaneously. Otherwise, the three phase arrangementincluding the control mechanism may be similar to that already-describedin connection witha single phase transformer.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. A transformer comprising a winding formed in two arallel connectedsections each provided with taps, a tap switch connected to the taps ofeach windin section, a circuit breaker in series with eac windingsection and its tap switch, means normally locking each ta switch aainst operation while its circuit reaker is c osed, and means forunlocking each tap switch to permit its tap connection to be changedwhile its circuit breaker is open.

2. A transformer comprising a winding iormed in two arallel connectedsections each provided with taps, a ta switch con- 3. A transformercomprising a winding formed in two parallel connected sections eachprovided With taps, a tap switch connected to the taps of each windingsection, a circuit breaker in series With each Winding section and itstap switch, each circuit breaker being provided with a tripping coil toopen it While its tap switch is being operated, and means responsive tothe opening of 10 each circuit breaker for opening the tripping coilcircuit of the other circuit breaker, whereby neither circuit breakercan be opened unless the other circuit breaker is closed and currentthrough the transformer cannot be interrupted by said circuit breakers.

In Witness whereof, We have hereunto set our hands this 31st day ofAugust 1925. HOWARD O. STEPHENS. ARTHUR PALME.

